[lojban] vocative production in PEG grammar

[".alyn.post." <alyn.post@lodockikumazvati.org>]

The PEG grammar has the following production:

vocative <- ( COI-clause NAI-clause? )+ DOI-clause
          / ( COI-clause NAI-clause? ) ( COI-clause NAI-clause? )*
          / DOI-clause

Which is a bit curious to me.  It *seems* like it could be
rewritten as:

vocative <- ( COI-clause NAI-clause? )* DOI-clause?

The only difference I can see between these two cases are that the
second form will match the empty string, whereas the first will not.
It looks like that is a problem for one of the ordered choices in the
'free' production.  (I'm not sure if that can be addressed yet.)

If vocative is written this way so that it does not match the empty
string, why isn't it written this way?:

vocative <- ( COI-clause NAI-clause? )+ DOI-clause
          / ( COI-clause NAI-clause? )+
          / DOI-clause

Where the second ordered choice uses the + operator instead of
FOO FOO*?

-Alan
-- 
.i ko djuno fi le do sevzi

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